A series of Cu-doped ZnIn2S4 photocatalysts has been synthesized by a facile hydrothermal method, with the copper concentration varying from 0 wt% to 2.0 wt%. The physical and photophysical properties of these Cu-doped ZnIn2S4 photocatalysts were characterized by X-ray diffraction (XRD), photoluminescence spectroscopy (PL), scanning electron microscopy (SEM), and UV−visible diffuse reflectance spectroscopy (UV−vis). The diffuse reflectance and photoluminescence spectra of Cu-doped ZnIn2S4 shifted monotonically to longer wavelengths as the copper concentration increased from 0 wt% to 2.0 wt%, indicating that the optical properties of these photocatalysts greatly depended on the amount of Cu doped. Meanwhile, the layered structure of ZnIn2S4 would be destructed gradually by Cu doping. The photoactivity of ZnIn2S4 was enhanced when Cu2+ was doped into the crystal structure. The highest photocatalytic activity was observed on Cu (0.5 wt%)–doped ZnIn2S4, with the rate of hydrogen evolution to be 151.5 μmol/h under visible light irradiation (λ > 430 nm). On the basis of the calculated energy band positions and optical properties, the effect of copper as a dopant on the photocatalytic activity of Cu-ZnIn2S4 was studied.